1. Field of the Invention
The present invention relates to a multitask control system, and more particularly to a control system for controlling operations of a plurality of controlled devices each capable of positioning a plurality of logical axes included therein to perform operations such as welding or assembling workpieces, wherein a parallel control of the respective devices is performed by a multitask processor, control of operations such as welding which require a real-time control by its nature is performed by a real-time processor.
2. Description of the Conventional Art
Various automatic apparatus including welding robots, assembling robots and so forth have heretofore been used in various manufacturing factories including automobile manufacturing lines. Generally, such automatic apparatus have positioning control capability for a plurality of logical axes in a welding gun or robot hand for welding or assembling workpieces, in which the positioning control is generally performed by a computer-based servomotor control system.
A typical automatic manufacturing line is composed of a plurality of automatic apparatus arranged along a processing sequence. The automatic apparatus are controlled individually or in combination for positioning or operation by a microprocessor-based sequencer or a computer-based controller.
Multitask control systems which are designed to control automatic apparatus of the type described above are disclosed in Japanese laid-open patent publications Nos. 63-86036 and 1-169540, for example. Here, multitask control refers to executing a plurality of tasks or jobs concurrently, by switching between tasks on a time-sharing basis each time an interrupt is entered. Real-time control refers to a process in which all of a series of necessary procedures including inputting, calculating, and outputting are completed until a next interrupt, and such processes are repeated each time an interrupt is entered.
Conventionally, target positions of respective axes (servomotors) included in a device have been given to a servomotor control system, and simultaneous arrival of the axes has been processed also on the servomotor control system side. Therefore, when there are a plurality of devices, the simultaneous arrival processing has to be repeated as many times as the number of devices, resulting in an increased amount of processing. Because an axis arrangement has to be altered by parameters, servo control processing is highly complex, and device processing is also complex.
When there are a plurality of devices to be controlled, it is preferable to use multitask processing to control respective devices concurrently. However, the multitask processing is not suited to control jobs which are real-time-oriented in their nature. If the controls of a plurality of devices are executed as a single task, the required description of a computer program becomes so complex that the reliability and performance of the program tend to be unsatisfactory. In addition, manpower required to develop and revise the program increases.